Bone and joint infections

Question 1

What is osteomyelitis?

Answer 1

Bone infection

Question 2

What is septic arthritis?

Answer 2

Joint infection

Question 3

What is prosthetic joint infection?

Answer 3

Infection of an artificial joint replacement

Question 4

What bacteria most commonly causes bone infections?

Answer 4

Staphylococcus Aureus

Question 5

What bacterias commonly cause infections of the bones and joints?

Answer 5

Staph Aureus (e.g. MRSA)
Streptococci
Enteric bacteria (e.g. E. Coli, Salmonella)
Coagulase-negative staphylococci (e.g. Staph Epidermis)
Mycobacterium tuberculosis

Question 6

What are the risk factors for developing a bone or joint infection?

Answer 6

Trauma, medical procedures, skin ulcers (direct inoculation)
Contagious spread (e.g. from nearby skin or soft tissue infection)
Haematogenous dissemination (e.g. through IV route)
Immunosuppression (e.g. DM, renal failure, sickle cell disease)

Question 7

What microbial factors need to be taken into account when determining the pathology of infections?

Answer 7

Access + Adherence (ability to reach and stick to site for invasion)
Invasion + Evasion (ability to penetrate barriers and evade immune system)
Multiplication
Resistance (to anti-microbial treatment)
Damage (to host cells)
Trasmission

Question 8

How does an acute infection develop into chronic osteomyelitis?

Answer 8

1. Initial infection localised to cortical region
2. Infection progression into sub-periosteal space with lifting of the periosteum
3. Diffuse infection with sequestrum (avascular necrotic region) and sinus tract (through which pus can escape)

Question 9

What is sequestrum?

Answer 9

When an infected bone becomes necrotic

Question 10

What is biofilm?

Answer 10

Bacteria in an organic matrix on an inert surface

Question 11

What is involucrum?

Answer 11

New bone formation outside sequestrum

Question 12

What is cloacae?

Answer 12

When pus from the sequestrum escapes through involucrum via holes

Question 13

What are discharging sinuses?

Answer 13

When infection and pus from cloacae causes skin necrosis

Question 14

What are the clinical features of osteomyelitis?

Answer 14

Pain, swelling, redness, warmth (typical of inflammation and therefore easy to misdiagnose)
Loss of function, fever, pathological fractures, discharging sinuses

Question 15

What are the clinical features of septic arthritis?

Answer 15

Pain, swelling, redness, warmth (typical of inflammation and therefore easy to misdiagnose)
Loss of function, fever, damage to articular surfaces

Question 16

What are common causes of osteomyelitis?

Answer 16

Traumatic infections (open fractures, penetrating wounds) 
Operative infections (joint replacements, internal fixation of fractures) 
Secondary to infections close to bones (e.g. burns, pressure ulcers) 
Contributing factors (e.g. vascular insufficiency due to diabetes or atherosclerosis)

Question 17

What investigations should be carried out for suspected bone or joint infections?

Answer 17

FBC + inflammatory markers (e.g. CRP)
Blood cultures (x2)
Skin/ ulcer swabs (e.g. for MRSA)
Imaging (e.g. plain radiographs, CT and MRI)
Joint and bone samples (e.g. joint aspiration, bone biopsy)

Question 18

When are plain radiographs a useful investigation?

Answer 18

Show late changes well but not early changes (such as periosteal reaction)

Question 19

When are CT scans useful as an investigation?

Answer 19

Useful for showing bone changes but not as useful for soft tissue changes

Question 20

When are MRI scans useful as an investigation?

Answer 20

Useful for showing soft tissue changes but not as useful for bone changes

Question 21

How is joint aspiration carried out?

Answer 21

Can be done on the ward under local anaesthetic

Single sample taken for microscopy, culture and PCR tests

Question 22

What might you see in joint fluid (that has been aspirated) in a patient with a joint infection?

Answer 22

Fluid may be non-viscous, turbid, purulent or blood-stained

Microscopy may show WBCs, bacteria or crystals

Question 23

How is a bone biopsy carried out?

Answer 23

Under general anaesthetic (in theatre)

Multiple samples taken for culture, PCR tests and histopathology

Question 24

How are bone and joint infections treated?

Answer 24

1. Manage sepsis
2. Obtain samples prior to starting abx (if possible)
3. Dependent on type of infection:

Septic arthritis requires joint washout in theatre
Osteomyelitis requires surgery if chronic changes present
Prosthetic joint infections require removal and replacement

Question 25

What antibiotics are used to treat bone and joint infections?

Answer 25

Empirical antibiotics = IV flucloxacillin + IV Benzylpenicillin
Targeted antibiotics are dependent on cultures and sensitivities

Question 26

How long should antibiotics be given for in the case of a bone or joint infection?

Answer 26

2-6 weeks IV

Further 4-6 weeks PO

Question 27

What prevention strategies should be in place to minimise bone and joint infections?

Answer 27

Prompt diagnosis and treatment or predisposing conditions
Strictest possible aseptic conditions for joint replacements
Antibiotics embedded into cement used for prosthetic joints